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DEEP SEA DIVING FROM AN ARM CHAIR:
USING AN ROV TO STUDY
MESOPELAGIC ECOLOGY
Kim R. Reisenbichler
and
Bruce H. Robison
Monterey Bay Aquarium Research Institute
160 Central Avenue
Pacific Grove, CA 93950
Since 1988, the Monterey Bay Aquarium Research Institute (MBARI) has
used a remotely operated vehicle (ROV) to study the ecology of Monterey Bay,
California. This vehicle has become a very useful platform for in situ observations of
mesopelagic zooplankton and their ecological interactions. Observations from our
ROV, as well as occasional dives in manned submersibles, have shown that the
mesopelagic community of Monterey Bay is much richer than previously believed,
when compared with data from conventional trawling surveys. Trawling data have
drastically underestimated the importance of gelatinous zooplankton at these depths
because they are so delicately constructed. Our ROV is particularly well suited to
stUdy
study these fragile organisms. Video data are collected by a broadcast-quality camera
and transmitted to the ship via optical fibers in the umbilical. Sensors on the MBARI
ROV include conductivity, temperature, depth, dissolved oxygen, a 563 KHz
scanning sonar and a fluorometer. Samplers currently include a variable speed, mu/tibinned suction sampler and four "detritus samplers" which allow an animal and a
volume of water to be enclosed and brought up to the surface undisturbed. We
ship/ROV operating system, the sensors and samplers currently
describe the MBARI ship/ROY
in use, give an overview of the organisms we are presently studying, and show that
the ROV is a useful tool for making the types of observations which were only recently
limited to blue water divers in shallow water.
INTRODUCTION
Until the latter part of this century, our understanding of the ecology of mesopelagic
communities was based solely on organisms collected by trawling surveys or by data from echo
communities
sounders. These data were then used to derive the structure and ecology of midwater communities.
communities.
sounders.
Unfortunately, data were biased towards the more robust animals such as fishes, crustaceans and
cephalopods which were not destroyed by being towed through the water at 100 cm! sec (2 knots) in
a mesh bag. The more delicate organisms, such as medusae, siphonphores and ctenophores, were
often either completely destroyed or appeared as disassociated parts.
As we began to make use of manned submersibles, especially those able to work in midwater
regions, the extent of the gap in our knowledge became obvious. A result has been that scientists
scientists
interested in midwater ecology began to request access to the vehicular platforms that allow them to
make in situ observations. Until recently only manned submersible were available for these purposes.
In response to this recognized need, and desiring to develop innovative technology, the
Monterey Bay Research Institute (MBARI) focused on the remotely operated vehicle (ROV) and
and
associated sensors and samplers. For the past three years MBARI has conducted ROV operations in
associated
Bay, California, using our research ship the RN Pt. LoOOs
Lobos and our ROV,
ROV. Ventana. This
Monterey Bay.
vehicle has developed into a very useful platform for in situ observations of mesopelagic
rnesopelagic zooplankton,
as well as organisms associated with the benthic communities of Monterey Bay. The following is a
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International Pacifica Scientific Diving... 1991
progress report on our research on the mesopelagic zooplankton and their ecological interactions.
MATERIALS AND METHODS
MBARI's oceanographic and ROV operations are conducted from the RIV
RN Pt. Lobos, a 33-m
(110-ft) converted oil field support ship. The nerve center of the ship is the ROV control room located
in the forepeak. The control room is set up comfortably for four cruise participants: the ROV
navigator,
achieved
navigator, ROV pilot, chief scientist and assistant scientist. Accurate ship/ROV navigation is achieved
with a Trimble Differential GPS system with an accuracy of ± 2 m for the ship and a Ferrante Trackpoint
IIII short baseline acoustical system for locating the ROV or other marked targets. The data from both
systems, as well as control data exported from the ROV control computer, is integrated, displayed and
stored by Meridian Ocean
OCean Systems software on a HP 370 mini computer. The control room also
contains controls and displays for a Mesotech scanning sonar, video camera and sampler software
controls, and a Seabird CTOD display and data logger.
Ventana is a Hysub 40, ATP1850, a hydraulically-driven vehicle powered by a 40 hp electric
motor with power supplied from the surface through an umbilical. The ROV has a maximum depth
capability of 1850 m. It was manufactured by International submarine Engineering of Port Moody,
British
British Columbia, Canada. Off-the-shelf equipment includes pitch, altitude and depth sensors, a
gyrocompass, a low light Osprey SIT camera, a single ISE manipulator arm, and a 653 KHz Mesotech
scanning sonar.
To adapt Ventana for scientific needs we added a number of sensors and samplers. Visual
data are provided by a broadcast quality Sony 3-chip CCD color video camera with 5.5 - 48 mm zoom
lens. Also, there are additional video inputs for peripheral cameras. Still photographs are taken with a
Photosea 1000 camera mounted with the video camera, and a Photosea DXT4000 stereo/macro
camera with video view finder. Physical oceanographic conditions are monitored with a Seabird CTOD
camera
transmissometer. Samplers currently include a
which can also be configured with a fluorometer and/or transmlssometer.
variable speed, multi-binned suction sampler capable of flow rates from 0 - 450 I/min (0 -120 gaL/min).
gaVmin).
variable
Low flow rates are used for delicate gelatinous organisms and high rates are required for strong
swimmers such as fish and squids. To collect fragile organisms in pristine condition, we have four 75-1
"detritus samplers" which allow the animal and a surrounding volume of water to be enclosed and
brought to the surface undisturbed and thermally insulated. Both types of the samplers are
manufactured by Harbor Branch Oceanographic Institution, Fort Pierce, Florida.
Data collected during each dive are of three types: navigation/orientation, video, and CTOD.
These data are collected on computers in the control room on a real-time basis. After each cruise, the
data are downloaded to a floppy disk and tape to be processed and stored in MBARI's data base
(Gritton, et al. 1989) for later access as needed.
RESULTS
We have found Ventanato
Ventana to be useful for making observations on a variety of animals. The first
category of animals are those which do not seem to be immediately affected by the presence of the
category
ROV, the gelatinous zooplankton. These include the larvaceans, medusae, ctenophores and
siphonophores. The second category of animals we observe are those which are aware of the
vehicle's presence and which approach it out of curiosity or are attracted to the lights. These include
vehicle's
some varieties of fish, cephalopods and crustaceans. We always keep in mind that observations of
some
the latter group are not necessarily observations of natural behavior. We are able to make
observations on vertical distribution, population density, swimming rates, sinking rates, feeding and
interactive behavior, individual size, and new taxa. We are currently focusing the attention of our
research group towards the gelatinous zooplankton.
Bathochordaeu5 charon, is a transparent, tadpole-shaped urochordate
The giant larvaceans, Bathochordaeus
itse". Our research has shown that these animals
that weaves a pair of structured mucous filters about itself.
make a significant contribution the vertical flux of organic carbon in the deep sea when they discard
the feeding filters that they use to collect their particulate food. These organically rich, large
aggregates sink at an average rate of 800 m per day, which is in sharp contrast to the typical pattem
pattern of
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Ec%gy
Reisenbich/er & Robison: ROV Studies of Mesope/agic Ecology
small, slowly sinking particles that are measured by conventional methods like sediment traps. Our
work has also shown for the first time, the details of the structure of the inner and outer filters and the
manner in which water and particulates flow through the system. We have also learned that, unlike the
smaller, shallow water larvaceans, Bathochordaeus continually produces the mucus that forms its
outer, coarse-mesh filter. These structures often grow quite large, sometimes as much as a meter in
largest dimension (Hamner and Robison, in press).
Siphonophores are elongate colonies of specialized individuals, whose relative importance in
mesopelagic ecosystems has been grossly underestimated by conventional sampling techniques.
Due to their gelatinous nature, and being an association of individuals, they tend to dissociate under
stressful conditions. Indeed, we have watched some species fall to pieces when disturbed by
nothing more than Ventana's lights. We are currently centering our attention on three siphonophores
common to Monterey Bay. Nanomia bijuga is a small, but abundant physonect siphonophore which
Ap/oemia sp., a physonect we see between 300 and 1000 m, is
we see throughout our depth range. Aploemia
a giant siphonophore whose sinuous body may be up to 40 m long. Praya sp. is another common
siphonophore in Monterey Bay. Praya can be found at depths between 250 and 400 m and may be
up to 3 m in length. Our research indicates that all of these siphonophores are much more numerous
than previously thought and that they feed heavily on other gelatinous animals as well as a variety of
small crustacean zooplankters that are subdued by their web of stinging tentacles.
Monterey Bay is host to a wide variety of medusae. Although we are not currently working on
medusa. we are able to make distribution and feeding observations when we see them.
any particular medusa,
So/missus, Atolla,
A few examples of medusae we can observe and collect for laboratory analysis are Solmissus,
Paraphylla, and C%bonema.
Colobonema. C/obonema
Clobonema is of particular interest due to an unusual behavior pattern;
when startled or agitated, it will often discard the majority of its iridescent, or perhaps bioluminescent,
tentacles and swim off, leaving its predator stung and confused.
Ctenophores are another group of animals whose importance to the rnidwater
midwater community has
been underestimated. Lobate ctenophores in particular, are so delicate that trawling surveys have
only revealed the most robust species. Surveys conducted using Ventana are finding that Monterey
Bay contains many more species than previously known. In fact, we recently described a new
species, Kiyohimea usagi, (Matsumoto and Robison 1991), and are investigating a recently collected
specimen which may represent an entirely new ctenophore family.
We also observe animals that respond to the vehicle. These animals may be attracted to the
lights or they may simply move in to feed on other organisms that are attracted. We observe
crustaceans such as euphausiids, copepods, amphipods, sergestids, pasaphasids and pelagic
isopods. The annelid worms are represented by docile organisms such as Poeobius sp., which
appear to simply float through the water feeding on particulates attached to mucous strands.
strands, or the
more elegantly active species such as tomopterids and alciopids which constantly paddle through the
regUlarly see a variety of squid species as well as the pelagic juvenile
water foraging for food. We also regularly
stage of Octopus rubescens.
Merluccius productus, is all too often a
A few fish are also attracted to Ventana. The hake, Mer/uccius
regular companion. Also, on rare occasions, we have had the opportunity to observe the king-of-thesalmon ribbonfish, Trachypterus a/tivelis,
a/tive/is, for extended periods of time. We have, however, had little
success trying to study most midwater fishes with Ventana.
SUMMARY AND CONCLUSIONS
The last three and one half years of operations using Ventana have proved that an ROV,
studying mesopelagic ecology. We have
when properly equipped and supported, is a useful tool for stUdying
studied, and are continuing to study, a variety of gelatinous zooplankton species as well as making
feeding and behavioral observations on other kinds of midwater animals.
Prior research, using electrically powered manned submersibles, has shown that studies of
midwater fish are possible in situ. This indicates that the most probable cause for lack of success
studying fish with Ventana is that the vehicle is powered by hydraulics. Hydraulic systems emit a
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International Pacifica Scientific Diving... 1991
continuous, high amplitude noise which may be responsible for the scarcity of most midwater fish.
The next generation MBARI vehicle, which is currently is the design phase, will be powered by electric
thrusters.
thrusters.
Before the end of 1991 we will be installing an accurate speedometer/odometer and an ultralow light video camera. These additions will enable us to better quantify our observations as well as to
begin studies of bioluminescence in the deep-sea.
LITERATURE CITED
Gritton,
Gritton, B., D. Badal, D. Davis, K. Lashkari, G. Morris, A. Pearce and H. Wright. 1989. Data
management of MBARI. Global Ocean, 5: 1681-1685.
Hamner, W.M. and B.H. Robison. 1991. In situ observations of giant appendicularians in Monterey
Bay. Deep-Sea Research, in press.
Matsumoto, G.1.
G.I. and B.H. Robison. 1991. Kiyohimea usagi, a new species of lobate ctenophore from
the Monterey submarine canyon. Bulletin of Marine Science, in press.
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